Trapped Mars Rover Finds Signs of Buried Martian Water in Recent Past

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NASA's stuck Mars rover Spirit has found more evidence that water
trickled beneath the Red Planet's surface in the past perhaps
within the last few hundred thousand years.

The sandy spot where Spirit got bogged down last year harbors
stratified layers of dirt with different compositions close to
the surface, a new study reveals. Researchers suspect these
layers were caused by seepage of thin films of
water on Mars, perhaps from melting frost or snow.

This seepage could have occurred during cyclical climate changes
when Mars was tilted more on its axis, researchers said. The
water may have moved down into the sand, carrying soluble
minerals deeper than less-soluble ones, they added. [ Most
Amazing Mars Rover Discoveries ]

The axis tilt of Mars varies over time scales of hundreds of
thousands of years. The fact that Spirit found these layers in
the dirt rather than locked away in rock further suggests the
water was seeping relatively recently, rather than billions of
years ago, researchers said.

"Once you freeze that evidence in a rock, it can stay there for a
long time," said Bruce Banerdt, a project scientist for the Mars
Exploration Rovers project at NASA's Jet Propulsion Laboratory in
Pasadena, Calif. "But you don't expect to maintain evidence in
loose dirt for long periods of time."

Buried water in Martian history

The relatively insoluble minerals near the surface include what
is thought to be hematite, silica and gypsum, according to
researchers. Iron-rich ferric sulfates, which are more soluble,
appear to have been dissolved and carried down deeper by water,
they added.

None of these minerals is exposed at the surface, which is
covered by wind-blown sand and dust.

"The lack of exposures at the surface indicates the preferential
dissolution of ferric sulfates must be a relatively recent and
ongoing process since wind has been systematically stripping soil
and altering landscapes in the region
Spirit has been examining," rover deputy principal
investigator Ray Arvidson of Washington University in St. Louis,
explained in a statement.

The new study, which appears in the Journal of Geophysical
Research, is based on observations made by Spirit before it
stopped communicating with Earth in March of this year. The
findings contribute to an accumulating set of evidence that Mars
may harbor small amounts of liquid water at some periods during
ongoing climate cycles.

Spirit, its rover twin Opportunity and other NASA Mars missions
have found evidence of wet Martian environments billions of years
ago that may have been favorable for life. Observations by the
Phoenix Mars Lander in 2008 and various orbiters since 2002
have identified buried layers of water ice at high and middle
latitudes and frozen water in polar ice caps.

Spirit still sleeping

The twin Mars rovers finished their three-month prime missions in
April 2004, then kept exploring in bonus missions. One of
Spirit's six wheels quit working in 2006.

In April 2009, Spirit's left wheels broke through a crust at a
site called "Troy" and churned into soft sand. A second wheel
stopped working seven months later. Spirit could not maneuver
into a position slanting its solar panels toward the sun for the
winter, as it had done for previous winters.

Engineers anticipated it would enter a low-power, silent
hibernation mode, and the
rover stopped communicating March 22 of this year. Spring
begins next month at Spirit's site, and NASA is listening to see
if the rover reawakens, officials said.

"Most of us have high hopes," Banerdt told SPACE.com. "Our models
say she could start communicating any day now. But we also
recognize that this is an extremely risky situation for Spirit,
and there are so many unknowns that we just can't be sure."

Among those unknowns, according to Banerdt: how much dust
blankets Spirit's solar panels, how cold the rover's interior got
and the current surface conditions where it bogged down.

Researchers took advantage of Spirit's months at Troy last year
to examine in great detail soil layers the wheels had exposed,
along with neighboring surfaces. Spirit made 13 inches of
progress in its last 10 backward drives before energy levels fell
too low for further driving in February.

Those drives exposed a new area of soil for possible examination
if Spirit does awaken and its robotic arm is still usable,
researchers said.

"With insufficient solar energy during the winter, Spirit goes
into a deep-sleep hibernation mode where all rover systems are
turned off, including the radio and survival heaters," said rover
project manager John Callas of JPL. "All available solar array
energy goes into charging the batteries and keeping the mission
clock running."

The rover is expected to have experienced temperatures colder
than it ever has before, and it may not survive. If Spirit does
get back to work, the top priority is a multi-month study that
can be done without driving the rover, researchers said.

The study would measure the rotation of Mars through the Doppler
signature of the stationary rover's radio signal with enough
precision to gain new information about the planet's core. The
rover Opportunity has been
making steady progress toward a large crater, Endeavour,
which is now approximately 5 miles away.